Millions of Joro Spiders Are Moving Up the East Coast. Here’s What to Expect

Worrisome headlines about venomous Joro spiders marching up the East Coast have been spreading across the Internet like, well, venomous Joro spiders marching up the East Coast.

The spiders are indeed on the move. The good news is that the headlines are circulating much faster than the creatures themselves. The better news is that these arachnids, also known as Trichonephila clavata, don’t readily bite, don’t kill humans and—contrary to some social media myths—can’t fly.

“They are not going to hurt you; they are not going to hurt your kids; they are not going to hurt your pets,” says Erin Grabarczyk, a biologist at Valdosta State University, who has studied the spiders’ dietary habits.

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Joro spiders are native to East Asia. They were introduced to the U.S. in 2013, when they were first spotted in Georgia, and probably arrived by hitching a ride on a shipping container, says Andy Davis, a University of Georgia scientist, who studies Joro spiders’ behavior and physiology. With their four-inch leg span, flashy black-and-yellow coloration and huge, golden-hued webs, these spiders aren’t subtle. But they’re also shy and docile. A 2023 study by Davis and one of his students, published in the journal Arthropoda, tested how several spider species reacted to a stressor (a light puff of air) and found that while most of them did so by freezing for under a minute, Joro spiders froze for more than an hour.

Ella Blakely, a fourth-year undergraduate student at Davis’s lab, can personally attest to the Joro’s retiring nature. For a study on whether Joro spiders eat native monarch butterflies that she co-authored with Davis, Blakely had to reach right into the arachnids’ webs to retrieve entangled butterflies. The spiders “would just kind of sit there,” she says. “They wouldn’t react, and they wouldn’t come out and bite us.”

Joro venom is made for subduing small insect prey, says Kelly Oten, a forest health researcher at North Carolina State University, who studies invasive species. The Joro spider’s bite, if you can manage to get one, is less painful than a bee sting and does not require medical intervention, Oten says.

It is true, however, that the Joro is on a probably unstoppable march to conquer the East Coast. There are now millions of these spiders in the Southeast, Davis says, and they are spreading. There have been some far-flung sightings, including in Oklahoma, Maryland and West Virginia, according to the community-science website Joro Watch, where individuals can report their own observations. Most of these have likely been one-off occurrences in which a spider had accidentally hitched a ride on a car, however. Without human assistance, Oten says, the spiders would naturally disperse at a rate of about 10 miles per year.

They mostly spread by “ballooning,” which involves using a thread of silk to catch the wind and float like a dandelion seed. This mode of transport has raised fears of airborne spider armies, but there’s no need to worry, Grabarczyk says. Joro spiders only balloon as young, tiny spiderlings. Adults are slow and awkward walkers when they are not on their webs.

Davis’s lab and others have found that the spiders are hardy and capable of surviving cold winters. Their native range takes them from chilly northern Japan to balmy Taiwan. “They’re very adept at living in a wide variety of climates, and those climates definitely overlap with what we see in the U.S. from Maine down to Florida,” Davis says. His research also finds that the spiders thrive in busy urban areas, including near roads and around buildings.

In other words, the spiders will likely make their way out of the Southeast into more northern states, and they’ll likely build webs in places where people will see them. This will probably happen more slowly than some of the headlines suggest, Oten says. “It’s not something the majority of the East Coast is going to have to worry about this year,” she says. “But in the next decade or so? Maybe.”

What is still a mystery is what impact the Joro spiders will have on the native ecosystem. Grabarczyk and her colleagues have found that Joro spiders generally chow down on whatever insects happen to fly by, she says. The arachnids would rather not eat monarch butterflies, whose bad-tasting toxins make them a last resort for spider snacks, which is a hint that one of North America’s most iconic insects will survive the Joro onslaught, says Emma Hobbs, who recently received a bachelor of science degree from the University of Georgia and co-authored the monarch study with Davis and Blakely. But researchers agree that more study is needed to find out whether Joro spiders will outcompete native spiders or otherwise damage East Coast ecology.

So far, the Joro spider doesn’t overlap in range with the spotted lanternfly (Lycorma delicatula), an invasive insect that coincidentally arrived in Pennsylvania from Asia around the same time the spider landed in the U.S. Southeast. It’s likely their ranges could overlap soon, though, Oten says, because both are now found in separate parts of North Carolina. When the two species do meet, it could be an interesting matchup Grabarczyk says. “I don’t think there’s any reason to think that [Joros] would not eat the spotted lanternfly.”

Because spotted lanternflies are an agricultural pest, people have been encouraged to kill them on sight. That’s not the situation with the Joro spider, which is better left alone, Davis says. “If it does take up residence in your backyard, it will be there for three or four months in the same place,” he says. “You can almost get to know that spider. Give it a name. Show your kids that spider. Show them what spiders do.… This almost gives you an unprecedented educational opportunity.”